Yes, modify by all means: The concept has ever only been to get the athlete to sprint for longer than they are required to do in the race they are planning to run. That is, if I am coaching a guy who can go around 45sec for 400m, I will work him for at least that long on the hills. So I have found a hill angle that doesn’t “damage” the racing mechanics, is firm but not hard under foot (grass or dirt not concrete or bitumen) and we open GPP with runs that average in the low to mid 50-sec range. The measurement of the hill worked out at around 360 metres.
There is explanation in more depth on the aspect in the “lactate threshold” thread
Anyway, suffice to say if you are targetting 60sec, you probably don’t really need them to be running hard for much more than 60sec - somewhere from 62 to 65 is good, and as they become fitter and less fearful you will see that time drop under 60sec, just as my 45sec guy’s times dropped from 52sec down to around 46-48sec as he developed the capacity to attack the hill.